There is already known an electrical programmer wherein a program carrier designed as a shaft carrying cam disks, individually scanned by spring assemblies, is intermittently driven by a continuously operating electric motor, especially a synchronous motor, via a camming sequencer. In that case there occurs in certain time intervals, e.g. of one or two minutes, an actuation of the stepping pawl and with it the advance of the cam-disk-carrying shaft by one incremental step. Supplemental devices are also known which make it possible to lift the stepping pawl, advancing the cam-disk-carrying shaft, during certain program phases out of its position of engagement with the ratchet wheel, in order to achieve in this way a program interruption dependent on physical parametric conditions. For this purpose there can be provided, for example, a small electromagnet which is energized for the duration of the contemplated program interruption and which lifts off the stepping pawl by attracting its armature.
A published further development of such a programmer is designed to permit a reduction of the step length of the program carrier during such advances of the program carrier which do not result in a change of the incremental states of the program, being thus more or less dependent on time, as against an increase in the step length upon performance of advances of the program carrier serving for a change in the incremental states of the program in order to provide a sufficient safety margin for carrying out the changeover.
Besides such program carriers, designed as cam-disk-carrying shafts, program carriers have also become known which, for example, are formed as flat program disks with concentric cam tracks, the latter being scanned by contact-lever assemblies arranged in groups.
In another known electrical programmer, use is made of two separate program carriers which, however, can be moved in mutual synchronism, or can even be interconnected or constitute a structural unit, for establishing or determining the incremental program states on the one hand and the duration of the individual program states on the other hand.
In this instance one may use wholly different time intervals, predeterminable by the program carrier, from one advance of the program carrier to the next, the program carrier being generally advanced or stepped only when a change in the incremental program state becomes necessary pursuant to the program.
Although these known electrical programmers have become fairly widely distributed, they are subjected in operation to mechanical wear and are bulky, i.e. require relatively much space, and their manufacture as well as repairs necessitate a careful adjustment of the control system constituting the programmer.
There is further required a considerable investment in components, especially transmission parts, associated with various contacts serving for the internal control of the programmer. These known devices are further characterized by a relatively high noise level during the evolution of the program.
An electrical programmer is also known wherein the interval from one advance of the program carrier to the next is determined by the automatic presetting of an electronic pulse counter, especially a frequency counter, in dependence upon the program-carrier disk, with the aid of contacts scanning same. This known electrical programmer, however, must also comprise numerous contacts which are necessary for the control of the internal switching operations of the device and which, of course, represent a certain expenditure and also an unpredictable source of troubles.